Effects of quercetin supplementation on glycemic control among patients with metabolic syndrome and related disorders: A systematic review and meta-analysis of randomized controlled trials

Efficacy and safety of dietary polyphenol administration as assessed by hormonal, glycolipid metabolism, inflammation and oxidative stress parameters in patients with PCOS: a meta-analysis and systematic review

BACKGROUND

The current knowledge about the efficacy and safety of dietary polyphenol administration in patients with polycystic ovarian syndrome (PCOS) is divergent.

OBJECTIVE

To evaluate the pooled efficacy and safety of dietary polyphenol administration in the treatment of patients with PCOS.

METHODS

The pubmed, Embase, Scopus, Cochrane Library, and Web of Science databases were searched for randomized controlled trials (RCTs) of dietary polyphenol administration for the treatment of PCOS. English-language RCTs involving adults with PCOS were thoroughly searched in electronic databases from the time of their establishment to May 2024. Random-effects models were used because heterogeneity was derived from differences in intervention materials and study duration, among other confounding factors. The effect sizes of the outcomes in the pooled analysis are expressed as weighted mean differences (WMDs) and 95% confidence intervals (CIs).

RESULTS

A total of 15 RCTs involving 934 patients were finally included. Compared with control treatments, dietary polyphenol administration significantly reduced luteinizing hormone (LH) (WMD: -0.85, 95% CI [-1.32 to -0.38], p = 0.00), and prolactin levels (WMD: -3.73, 95% CI [-6.73 to -0.74], p = 0.01). Dietary polyphenol administration significantly reduced insulin levels (WMD: -0.85, 95% CI [-1.32 to -0.38], p = 0.00). Regarding lipid metabolism, dietary polyphenol administration only reduced triglyceride levels (WMD: -8.96, 95% CI [-16.44 to -1.49], p = 0.02). Malondialdehyde (MDA) (WMD: -0.65, 95% CI [-0.68 to -0.62], p = 0.00), tumor necrosis factor (TNF-α) (WMD: -1.39, 95% CI [-2.41 to -0.37], p = 0.01) concentrations were significantly reduced by dietary polyphenol administration. None of the interventions significantly affected weight, body mass index (BMI), waist circumference (WC), homeostatic model-insulin resistance (HOMA-IR), fasting blood sugar (FBS), glycated hemoglobin (HBA1c), follicle-stimulating hormone (FSH), testosterone (T), dehydroepiandrosterone (DHEA), estradiol (E2), anti-Müllerian hormone (AMH), quantitative insulin-sensitivity check index (QUICKI), sex hormone-binding globulin (SHBG), total antioxidant capacity (TAC), C-peptide, C-reactive protein (CRP), high-density lipoprotein (HDL), low-density lipoprotein (LDL), cholesterol, cholesterol/HDL, acne score, thyroid-stimulating hormone (TSH), aspartate aminotransferase (AST), alanine aminotransferase (ALT) or alkaline phosphatase (ALP).

CONCLUSION

Dietary polyphenol administration was efficacious in patients with PCOS in our study. This review might provide new insight into the treatment of patients with PCOS and the potential of daily polyphenol supplementation in patients with PCOS. Nevertheless, these results must be interpreted carefully as a result of the heterogeneity and risk of bias among the studies and we expect that more high-quality RCTs evaluating the efficacy and safety of dietary polyphenol adnimistration in patients with PCOS will be conducted in the future.

SYSTEMATIC REVIEW REGISTRATION

CRD42024498494.

Mechanistic insights into antidiabetic potential of Ficus viren against multi organ specific diabetic targets: molecular docking, MDS, MM-GBSA analysis

Ficus viren has been traditionally used to treat diabetes, and its extract inhibits carbohydrate/lipid metabolism and possesses anti-hyperglycemic potential. However, there is conflicting investigation related to F. viren extract effect on carbohydrate metabolism. Thus, bioactive and mechanism behind its antidiabetic potential is still scanty. This study explored F. viren's anti-diabetic property by identifying potential phytoconstituents and mechanism. A sequential in-silico approach was used i.e., druglikeness, molecular docking, post-docking MM-GBSA, ADMET studies, molecular dynamic simulation (MDS), and post-MDS MM-GBSA. We screened ∼32 phytoconstituents and twelve potential organ-specific diabetic targets (O.S.D.Ts i.e., IR, DPP-4, ppar-γ, ppar-α, ppar-δ, GLP-1R, SIRT-1, AMPK, GSK-3β, RAGE, and AR). Drug likeness study identified 18 druggable candidates among 32 phytoconstituents. K3A, quercetin, scutellarein, sorbifolin, and vogeline J identified as potential ligands from druggable ligands, using IR as the standard target. Subsequently, potential ligands docked with remaining O.S.D.Ts. and data showed that K3A binds strongly with AMPK, ppar-δ, DPP-4, and GSK-3β, while scutellarein binds with AR and ppar-α. Sorbifolin, quercetin, and vogeline J binds with ppar-α, ppar-γ, and RAGE, respectively. Post-docking MM-GBSA data (∆GBind) also depicted potential ligand's strong binding affinities with their corresponding targets. Thereafter, simulation data revealed that only scutellarein and sorbifolin showed dynamic stability with their respective targets, i.e., AR/ppar-α and ppar-α, respectively. Interestingly, post-MDS MM-GBSA revealed that only scutellarein exhibited strong ∆GBind of -55.08 kcal/mol and -75.48 kcal/mol with AR and ppar-α, respectively. Though, collective computational analysis supports antidiabetic potential of F. viren through AR and ppar-α modulation by scutellarein.

Quercetin intervention reduced hepatic fat deposition in patients with nonalcoholic fatty liver disease: a randomized, double-blind, placebo-controlled crossover clinical trial

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) has become a growing public health problem worldwide. However, there is still lack of effective treatment strategies except lifestyle intervention.

OBJECTIVES

To evaluate whether quercetin improves intrahepatic lipid content in patients with NAFLD.

METHODS

In this randomized, double-blind, placebo-controlled crossover trial, 41 patients with NAFLD were randomly assigned to receive the quercetin (500 mg) or placebo capsules for 12 wk, then switched interventions for another 12 wk after a 4-wk washout period. The primary outcome was intrahepatic lipid content evaluated by magnetic resonance imaging estimated proton density fat fraction. The secondary outcomes were liver function measurements, etc. Safety outcomes included blood routine.

RESULTS

A total of 36 patients completed the trial. In intention-to-treat analyses, the quercetin intervention moderately decreased the intrahepatic lipid contents from 11.5% ± 6.4% to 9.6% ± 5.8%, compared with the placebo intervention (decreased by 0.1% ± 2.6%, P = 0.013 and adjusted P value is 0.028). Body weight and body mass index were mildly reduced by 1.5 ± 2.6 kg and 0.5 ± 0.9 kg/m2 after the quercetin intervention (P < 0.05 and both adjusted P values are 0.038), whereas the reductions were only 0.2 ± 1.8 kg and 0.1 ± 0.7 kg/m2 after the placebo intervention. The intrahepatic lipid content reductions were noticeably positively associated with the body weight losses after the quercetin and placebo interventions (r = 0.557 and 0.412, P < 0.001 and P = 0.007, respectively). Subgroup analyses found that the reduction of intrahepatic lipid contents in females (3.0% ± 3.7%) was about twice as large as that in males (1.4% ± 2.5%) with a trend of statistical significance (P = 0.113 and adjusted P value is 0.061). There were no significant differences in other secondary and safety outcomes. No adverse events associated with study intervention were found.

CONCLUSIONS

Twelve weeks treatment of quercetin could reduce intrahepatic lipid contents in patients with NAFLD, possibly explained by a slightly larger body weight loss in the quercetin group.

TRIAL REGISTRATION

The trial is registered at www.chictr.org.cn as ChiCTR2100047904.

New perspectives on the therapeutic potential of quercetin in non-communicable diseases: Targeting Nrf2 to counteract oxidative stress and inflammation

Non-communicable diseases (NCDs), including cardiovascular diseases, cancer, metabolic diseases, and skeletal diseases, pose significant challenges to public health worldwide. The complex pathogenesis of these diseases is closely linked to oxidative stress and inflammatory damage. Nuclear factor erythroid 2-related factor 2 (Nrf2), a critical transcription factor, plays an important role in regulating antioxidant and anti-inflammatory responses to protect the cells from oxidative damage and inflammation-mediated injury. Therefore, Nrf2-targeting therapies hold promise for preventing and treating NCDs. Quercetin (Que) is a widely available flavonoid that has significant antioxidant and anti-inflammatory properties. It modulates the Nrf2 signaling pathway to ameliorate oxidative stress and inflammation. Que modulates mitochondrial function, apoptosis, autophagy, and cell damage biomarkers to regulate oxidative stress and inflammation, highlighting its efficacy as a therapeutic agent against NCDs. Here, we discussed, for the first time, the close association between NCD pathogenesis and the Nrf2 signaling pathway, involved in neurodegenerative diseases (NDDs), cardiovascular disease, cancers, organ damage, and bone damage. Furthermore, we reviewed the availability, pharmacokinetics, pharmaceutics, and therapeutic applications of Que in treating NCDs. In addition, we focused on the challenges and prospects for its clinical use. Que represents a promising candidate for the treatment of NCDs due to its Nrf2-targeting properties.

Exploring the therapeutic potential of quercetin: A focus on its sirtuin-mediated benefits

As the global population ages, preventing lifestyle- and aging-related diseases is increasing, necessitating the search for safe and affordable therapeutic interventions. Among nutraceuticals, quercetin, a flavonoid ubiquitously present in various plants, has garnered considerable interest. This review aimed to collate and analyze existing literature on the therapeutic potentials of quercetin, especially its interactions with SIRTs and its clinical applicability based on its bioavailability and safety. This narrative review was based on a literature survey spanning from 2015 to 2023 using PUBMED. The keywords and MeSH terms used were: "quercetin" AND "bioavailability" OR "metabolism" OR "metabolites" as well as "quercetin" AND "SIRTuin" OR "SIRT*" AND "cellular effects" OR "pathway" OR "signaling" OR "neuroprotective" OR "cardioprotective" OR "nephroprotective" OR "antiatherosclerosis" OR "diabetes" OR "antidiabetic" OR "dyslipidemia" AND "mice" OR "rats". Quercetin demonstrates multiple therapeutic activities, including neuroprotective, cardioprotective, and anti-atherosclerotic effects. Its antioxidant, anti-inflammatory, antiviral, and immunomodulatory properties are well-established. At a molecular level, it majorly interacts with SIRTs, particularly SIRT1 and SIRT6, and modulates numerous signaling pathways, contributing to its therapeutic effects. These pathways play roles in reducing oxidative stress, inflammation, autophagy regulation, mitochondrial biogenesis, glucose utilization, fatty acid oxidation, and genome stability. However, clinical trials on quercetin's effectiveness in humans are scarce. Quercetin exhibits a wide range of SIRT-mediated therapeutic effects. Despite the compelling preclinical data, more standardized clinical trials are needed to fully understand its therapeutic potential. Future research should focus on addressing its bioavailability and safety concerns.

Biomarkers and signaling pathways of diabetic nephropathy and peripheral neuropathy: possible therapeutic intervention of rutin and quercetin

Diabetic nephropathy and peripheral neuropathy are the two main complications of chronic diabetes that contribute to high morbidity and mortality. These conditions are characterized by the dysregulation of multiple molecular signaling pathways and the presence of specific biomarkers such as inflammatory cytokines, indicators of oxidative stress, and components of the renin-angiotensin system. In this review, we systematically collected and collated the relevant information from MEDLINE, EMBASE, ELSEVIER, PUBMED, GOOGLE, WEB OF SCIENCE, and SCOPUS databases. This review was conceived with primary objective of revealing the functions of these biomarkers and signaling pathways in the initiation and progression of diabetic nephropathy and peripheral neuropathy. We also highlighted the potential therapeutic effectiveness of rutin and quercetin, two plant-derived flavonoids known for their antioxidant and anti-inflammatory properties. The findings of our study demonstrated that both flavonoids can regulate important disease-promoting systems, such as inflammation, oxidative stress, and dysregulation of the renin-angiotensin system. Importantly, rutin and quercetin have shown protective benefits against nephropathy and neuropathy in diabetic animal models, suggesting them as potential therapeutic agents. These findings provide a solid foundation for further comprehensive investigations and clinical trials to evaluate the potential of rutin and quercetin in the management of diabetic nephropathy and peripheral neuropathy. This may contribute to the development of more efficient and comprehensive treatment approaches for diabetes-associated complications.

The impact of consuming technologically processed functional foods enriched/fortified with (poly)phenols on cardiometabolic risk factors: a systematic review of randomized controlled trials

Cardiovascular diseases are a major global cause of death and healthcare costs, emphasizing the need for effective prevention and management of cardiometabolic risk factors. One promising approach is the consumption of technologically processed functional foods enriched/fortified with (poly)phenols. The current systematic review aimed to evaluate the human clinical trials evidence on the effect of intake of these foods on reducing the most common cardiometabolic risk factors. 12 randomized controlled studies were included in the systematic review, with varying food intake amounts (27-360 g/day) and (poly)phenol doses (32.5-850 mg/day). These interventions included consumption of functional bakery goods, cereal bars, pasta, chocolate, and yogurt, with supplementation periods spanning from 2 to 52 wk. Several foods, such as green tea extract-fortified rye bread and olive fruit (poly)phenol-fortified yogurt, significantly lowered blood pressure. Flavonoid-enriched chocolate, hydroxytyrosol-fortified bread, and other products influenced glucose metabolism. Additionally, various functional foods were associated with improved blood lipid levels. While these results indicate the health advantages of consuming technologically processed functional foods enriched/fortified with (poly)phenols, caution is warranted due to the scarcity and limitations of existing studies. Further research is needed to confirm and expand upon these results in the prevention and management of cardiometabolic risk factors.

Role of Quercetin in DNA Repair: Possible Target to Combat Drug Resistance in Diabetes

Diabetes Mellitus (DM) is referred to as hyperglycemia in either fasting or postprandial phases. Oxidative stress, which is defined by an excessive amount of reactive oxygen species (ROS) production, increased exposure to external stress, and an excessive amount of the cellular defense system against them, results in cellular damage. Increased DNA damage is one of the main causes of genomic instability, and genetic changes are an underlying factor in the emergence of cancer. Through covalent connections with DNA and proteins, quercetin has been demonstrated to offer protection against the creation of oxidative DNA damage. It has been found that quercetin shields DNA from possible oxidative stress-related harm by reducing the production of ROS. Therefore, Quercetin helps to lessen DNA damage and improve the ability of DNA repair mechanisms. This review mainly focuses on the role of quercetin in repairing DNA damage and compensating for drug resistance in diabetic patients. Data on the target topic was obtained from major scientific databases, including SpringerLink, Web of Science, Google Scholar, Medline Plus, PubMed, Science Direct, and Elsevier. In preclinical studies, quercetin guards against DNA deterioration by regulating the degree of lipid peroxidation and enhancing the antioxidant defense system. By reactivating antioxidant enzymes, decreasing ROS levels, and decreasing the levels of 8-hydroxydeoxyguanosine, Quercetin protects DNA from oxidative damage. In clinical studies, it was found that quercetin supplementation was related to increased antioxidant capacity and decreased risk of type 2 diabetes mellitus in the experimental group as compared to the placebo group. It is concluded that quercetin has a significant role in DNA repair in order to overcome drug resistance in diabetes.

The effect of quercetin supplementation on clinical outcomes in COVID-19 patients: A systematic review and meta-analysis

Coronavirus disease (COVID-19) affects both the respiratory system and the body as a whole. Natural molecules, such as flavonoid quercetin, as potential treatment methods to help patients combat COVID-19. The aim of this systematic review and meta-analysis is to give a comprehensive overview of the impact of quercetin supplementation on inflammatory factors, hospital admission, and mortality of patients with COVID-19. The search has been conducted on PubMed, Scopus, Web of Science, EMBASE, and the Cochrane Library using relevant keywords until August 25, 2023. We included randomized controlled trials (RCTs) comparing COVID-19 patients who received quercetin supplementation versus controls. We included five studies summarizing the evidence in 544 patients. Meta-analysis showed that quercetin administration significantly reduced LDH activity (standard mean difference (SMD): -0.42, 95% CI: -0.82, -0.02, I 2 = 48.86%), decreased the risk of hospital admission by 70% (RR: 0.30, 95% CI: 0.14, 0.62, I 2 = 00.00%), ICU admission by 73% (RR: 0.27, 95% CI: 0.09, 0.78, I 2 = 20.66%), and mortality by 82% (RR: 0.18, 95% CI: 0.03, 0.98, I 2 = 00.00%). No significant changes in CRP, D-dimmer, and ferritin were found between groups. Quercetin was found to significantly reduce LDH levels and decrease the risk of hospital and ICU admission and mortality in patients with COVID-19 infection.

Flavonols as a Potential Pharmacological Intervention for Alleviating Cognitive Decline in Diabetes: Evidence from Preclinical Studies

Diabetes mellitus is a complex metabolic disease associated with reduced synaptic plasticity, atrophy of the hippocampus, and cognitive decline. Cognitive impairment results from several pathological mechanisms, including increased levels of advanced glycation end products (AGEs) and their receptors, prolonged oxidative stress and impaired activity of endogenous mechanisms of antioxidant defense, neuroinflammation driven by the nuclear factor kappa-light-chain enhancer of activated B cells (NF-κB), decreased expression of brain-derived neurotrophic factor (BDNF), and disturbance of signaling pathways involved in neuronal survival and cognitive functioning. There is increasing evidence that dietary interventions can reduce the risk of various diabetic complications. In this context, flavonols, a highly abundant class of flavonoids in the human diet, are appreciated as a potential pharmacological intervention against cognitive decline in diabetes. In preclinical studies, flavonols have shown neuroprotective, antioxidative, anti-inflammatory, and memory-enhancing properties based on their ability to regulate glucose levels, attenuate oxidative stress and inflammation, promote the expression of neurotrophic factors, and regulate signaling pathways. The present review gives an overview of the molecular mechanisms involved in diabetes-induced cognitive dysfunctions and the results of preclinical studies showing that flavonols have the ability to alleviate cognitive impairment. Although the results from animal studies are promising, clinical and epidemiological studies are still needed to advance our knowledge on the potential of flavonols to improve cognitive decline in diabetic patients.

Quercetin as a Therapeutic Product: Evaluation of Its Pharmacological Action and Clinical Applications-A Review

Quercetin is the major polyphenolic flavonoid that belongs to the class called flavanols. It is found in many foods, such as green tea, cranberry, apple, onions, asparagus, radish leaves, buckwheat, blueberry, broccoli, and coriander. It occurs in many different forms, but the most abundant quercetin derivatives are glycosides and ethers, namely, Quercetin 3-O-glycoside, Quercetin 3-sulfate, Quercetin 3-glucuronide, and Quercetin 3'-metylether. Quercetin has antioxidant, anti-inflammatory, cardioprotective, antiviral, and antibacterial effects. It is found to be beneficial against cardiovascular diseases, cancer, diabetes, neuro-degenerative diseases, allergy asthma, peptic ulcers, osteoporosis, arthritis, and eye disorders. In pre-clinical and clinical investigations, its impacts on various signaling pathways and molecular targets have demonstrated favorable benefits for the activities mentioned above, and some global clinical trials have been conducted to validate its therapeutic profile. It is also utilized as a nutraceutical due to its pharmacological properties. Although quercetin has several pharmacological benefits, its clinical use is restricted due to its poor water solubility, substantial first-pass metabolism, and consequent low bioavailability. To circumvent this limited bioavailability, a quercetin-based nanoformulation has been considered in recent times as it manifests increased quercetin uptake by the epithelial system and enhances the delivery of quercetin to the target site. This review mainly focuses on pharmacological action, clinical trials, patents, marketed products, and approaches to improving the bioavailability of quercetin with the use of a nanoformulation.

The effects of Quercetin supplementation on cardiometabolic outcomes: An umbrella review of meta-analyses of randomized controlled trials

BACKGROUND

Quercetin is a bioactive flavonoid, but the effect of it on cardiometabolic factors has remained uncertain and previous findings from meta-analyses have been controversial.

OBJECTIVE

To provide an overview of the effects of Quercetin on cardiometabolic factors based on meta-analyses of randomized controlled trials (RCTs).

METHOD

MEDLINE, SciVerse Scopus, and Clarivate Analytics Web of Science databases were searched to identify eligible publications. As part of the umbrella review, we summarized pooled estimates, 95% CIs, heterogeneity, and publication bias. A GRADE (Grading of Recommendations Assessment, Development, and Evaluation) approach was used to rate the certainty of evidence.

RESULTS

Five meta-analyses including 18 eligible RCTs plus 5 RCTs that were not included in previous meta-analyses were found. The results indicated Quercetin does not affect diastolic blood pressure (DBP), lipid profile, inflammation, anthropometric indices, fasting plasma glucose (FBG), and homeostatic model assessment for insulin resistance (HOMA-IR). However, Quercetin supplementation could significantly reduce systolic blood pressure (SBP) (weighted mean difference (WMD): -1.9, 95% CI = -3.2 to -0.6, I2  = 88.3%) and insulin level (WMD: -1.07, 95% CI = -1.9 to -0.1, I2  = 75.0%). The certainty of evidence ranged from very low to moderate.

CONCLUSION

Quercetin supplementation has reducing effects on SBP and insulin levels but not other cardiometabolic parameters. More high-quality trials with longer follow-up durations may be required to obtain a more robust conclusion.

Impact of Polyphenols on Inflammatory and Oxidative Stress Factors in Diabetes Mellitus: Nutritional Antioxidants and Their Application in Improving Antidiabetic Therapy

Diabetes mellitus is a chronic metabolic disorder characterized by hyperglycaemia and oxidative stress. Oxidative stress plays a crucial role in the development and progression of diabetes and its complications. Nutritional antioxidants derived from dietary sources have gained significant attention due to their potential to improve antidiabetic therapy. This review will delve into the world of polyphenols, investigating their origins in plants, metabolism in the human body, and relevance to the antioxidant mechanism in the context of improving antidiabetic therapy by attenuating oxidative stress, improving insulin sensitivity, and preserving β-cell function. The potential mechanisms of, clinical evidence for, and future perspectives on nutritional antioxidants as adjuvant therapy in diabetes management are discussed.

A Descriptive Review of the Action Mechanisms of Berberine, Quercetin and Silymarin on Insulin Resistance/Hyperinsulinemia and Cardiovascular Prevention

Insulin resistance (IR) and the associated hyperinsulinemia are early pathophysiological changes which, if not well treated, can lead to type 2 diabetes, endothelial dysfunction and cardiovascular disease. While diabetes care is fairly well standardized, the prevention and treatment of IR lacks a single pharmaceutical approach and many lifestyle and dietary interventions have been proposed, including a wide range of food supplements. Among the most interesting and well-known natural remedies, alkaloid berberine and the flavonol quercetin have particular relevance in the literature, while silymarin-the active principle of the Silybum marianum thistle-was traditionally used for lipid metabolism disorders and to sustain liver function. This review describes the major defects of insulin signaling leading to IR and the main properties of the three mentioned natural substances, their molecular targets and synergistic action mechanisms. The actions of berberine, quercetin and silymarin are partially superimposable as remedies against reactive oxygen intermediates generated by a high-lipid diet and by NADPH oxidase, which is triggered by phagocyte activation. Furthermore, these compounds inhibit the secretion of a battery of pro-inflammatory cytokines, modulate intestinal microbiota and are especially able to control the various disorders of the insulin receptor and post-receptor signaling systems. Although most of the evidence on the effects of berberine, quercetin and silymarin in modulating insulin resistance and preventing cardiovascular disease derive from experimental studies on animals, the amount of pre-clinical knowledge strongly suggests the need to investigate the therapeutic potential of these substances in human pathology.

Apple Peel Supplementation Potential in Metabolic Syndrome Prevention

(1) Introduction: Apples are a source of bioactive substances, e.g., anthocyanidins and flavonols, and dietary fiber. Their highest concentrations are observed in the skin. Metabolic syndrome (MetS) is a set of conditions originally associated with obesity. Excessive adipose tissue accompanying obesity leads to chronic inflammation and metabolic disorders, which result in the development of dyslipidemia, elevated blood pressure, and glucose levels. Thus, supplementation of apple peels, a source of antioxidant substances and fiber, could potentially be a method supporting the prevention of MetS. This paper summarizes the results of available research on the potential impact of apple peel supplementation on the components of MetS. (2) Results: The results from in vitro and animal model studies indicate a positive effect of apple peel supplementation on lipid profile, glucose levels, and blood pressure regulation mediators. Only one human study was performed, and it showed that the consumption of apple peels had an effect on endothelial function but not on other clinical parameters. At the moment, there are no results from observations on large groups of people available. (3) Conclusions: The results of in vitro and animal-model studies indicate the potential of apple peel supplementation in MetS prevention, but it has not been clinically confirmed in human studies. Conducting large human studies could allow a definite clarification of the role of apple peel supplementation in MetS prevention.

Bio-Actives from Natural Products with Potential Cardioprotective Properties: Isolation, Identification, and Pharmacological Actions of Apigenin, Quercetin, and Silibinin

Cardiovascular diseases (CVDs) are the leading cause of morbidity and mortality worldwide. As a result, pharmaceutical and non-pharmaceutical interventions modifying risk factors for CVDs are a top priority of scientific research. Non-pharmaceutical therapeutical approaches, including herbal supplements, have gained growing interest from researchers as part of the therapeutic strategies for primary or secondary prevention of CVDs. Several experimental studies have supported the potential effects of apigenin, quercetin, and silibinin as beneficial supplements in cohorts at risk of CVDs. Accordingly, this comprehensive review focused critically on the cardioprotective effects/mechanisms of the abovementioned three bio-active compounds from natural products. For this purpose, we have included in vitro, preclinical, and clinical studies associated with atherosclerosis and a wide variety of cardiovascular risk factors (hypertension, diabetes, dyslipidemia, obesity, cardiac injury, and metabolic syndrome). In addition, we attempted to summarize and categorize the laboratory methods for their isolation and identification from plant extracts. This review unveiled many uncertainties which are still unexplored, such as the extrapolation of experimental results to clinical practice, mainly due to the small clinical studies, heterogeneous doses, divergent constituents, and the absence of pharmacodynamic/pharmacokinetic analyses.

Quercetin and polycystic ovary syndrome; inflammation, hormonal parameters and pregnancy outcome: A randomized clinical trial

PROBLEM

Women with PCOS have a reduced total antioxidant level in addition to higher oxidative stress. Quercetin is a flavonol-type antioxidant that may be found in many foods. Does quercetin affect inflammatory and hormonal factors and clinical outcomes in PCOS patients?

METHOD OF STUDY

Seventy-two women with PCOS were randomly allocated to one of two intervention groups, and each received a daily dosage of 500 mg of Quercetin for the intervention group or a placebo for the control group for a period of 40 days from the start of the menstrual cycle until the day of ovulation. Serum levels of IL-6, TNF-alpha, LH, FSH, and AMH were measured using ELISA. In addition, oocyte and embryo grade before IVF and pregnancy rate have been examined.

RESULTS

LH levels reduce significantly in the quercetin group (4.351.62 at baseline to 3.061.43 after 3 months) (p = .029). The results indicated that Quercetin significantly decreased TNF alpha levels in comparison to the pretest (p = .008). Following capsule administration, IL-6 levels significantly decreased in the quercetin group (p = .001). Except for Δ LH, ΔIL6, and ΔFSH, there was no significant difference in any of the hormones and inflammations parameter changes.

CONCLUSION

Quercetin consumption causes improvement in oocyte and embryo grade and the pregnancy rate in PCOS patients. As a result, regular consumption of Quercetin has been shown to decrease inflammatory and LH parameters, making it beneficial for the management of PCOS and related diseases.

Quercetin ameliorates hepatic fat accumulation in high-fat diet-induced obese mice via PPARs

As a natural pigment in food, quercetin possesses multiple biological activities and plays a crucial role in regulating metabolic syndrome. Herein, we aim to explore the potential mechanism of quercetin to ameliorate hepatic fat accumulation. In vivo experiments showed that quercetin significantly relieved inflammation response by decreasing the serum TNF-α and IL-6 levels and also improved high-fat diet-induced hepatic steatosis without other organ injuries. Quercetin can effectively reduce lipid aggregation and down-regulate the protein expression of PCK1 in HepG2 cells induced by oleic acid and palmitic acid, indicating that inhibiting gluconeogenesis leads to hepatic fat accumulation reduction. Furthermore, molecular docking results suggested that quercetin can bind to both PPARα and PPARγ, with an even more potent binding affinity than indeglitazar, a pan-agonist of PPARs. In conclusion, quercetin may regulate gluconeogenesis to ameliorate hepatic fat accumulation via targeting PPARα/γ.

An investigation into the potential action of polyphenols against human Islet Amyloid Polypeptide aggregation in type 2 diabetes

Type 2 diabetes (T2D), a chronic metabolic disease characterized by hyperglycemia, results in significant disease burden and financial costs globally. Whilst the majority of T2D cases seem to have a genetic basis, non-genetic modifiable and non-modifiable risk factors for T2D include obesity, diet, physical activity and lifestyle, smoking, age, ethnicity, and mental stress. In healthy individuals, insulin secretion from pancreatic islet β-cells is responsible for keeping blood glucose levels within normal ranges. T2D patients suffer from multifactorial onset of β-cell dysfunction and/or loss of β-cell mass owing to reactive oxygen species (ROS) production, mitochondrial dysfunction, autophagy, and endoplasmic reticulum (ER) stress. Most predominantly however, and the focus of this review, it is the aggregation and misfolding of human Islet Amyloid Polypeptide (hIAPP, also known as amylin), which is detrimental to β-cell function and health. Whilst hIAPP is found in healthy individuals, its misfolded version is cytotoxic and able to induce β-cell dysfunction and/or death through various mechanisms including membrane changes in β-cell causing influx of calcium ions, arresting complete granule membrane recovery and ER stress. There are several existing therapeutics for T2D. However, there is a need for alternative or adjunct therapies for T2D with milder adverse effects and greater availability. Foremost among the potential natural therapeutics are polyphenols. Extensive data from studies evaluating the potential of polyphenols to inhibit hIAPP aggregation and disassemble aggregated hIAPP are promising. Moreover, in-vivo, and in-silico studies also highlight the potential effects of polyphenols against hIAPP aggregation and mitigation of larger pathological effects of T2D. Whilst there have been some promising clinical studies on the therapeutic potential of polyphenols, extensive further clinical studies and in-vitro studies evaluating the mechanisms of action and ideal doses for many of these compounds are required. The need for these studies is made more important by the postulated link between Alzheimer's disease (AD) and T2D pathophysiology given the similar aggregation process of their respective amyloid proteins, which evokes thoughts of cross-reactive polyphenols which can be effective for both AD and T2D patients.

The role of dietary antioxidants in type 2 diabetes and neurodegenerative disorders: An assessment of the benefit profile

Healthy diet is vital to cellular health. The human body succumbs to numerous diseases which afflict severe economic and psychological burdens on the patient and family. Oxidative stress is a possible crucial regulator of various pathologies, including type 2 diabetes and neurodegenerative diseases. It generates reactive oxygen species (ROS) that trigger the dysregulation of essential cellular functions, ultimately affecting cellular health and homeostasis. However, lower levels of ROS can be advantageous and are implicated in a variety of signaling pathways. Due to this dichotomy, the terms oxidative "eustress," which refers to a good oxidative event, and "distress," which can be hazardous, have developed. ROS affects multiple signaling pathways, leading to compromised insulin secretion, insulin resistance, and β-cell dysfunction in diabetes. ROS is also associated with increased mitochondrial dysfunction and neuroinflammation, aggravating neurodegenerative conditions in the body, particularly with age. Treatment includes drugs/therapies often associated with dependence, side effects including non-selectivity, and possible toxicity, particularly in the long run. It is imperative to explore alternative medicines as an adjunct therapy, utilizing natural remedies/resources to avoid all the possible harms. Antioxidants are vital components of our body that fight disease by reducing oxidative stress or nullifying the excess toxic free radicals produced under various pathological conditions. In this review, we focus on the antioxidant effects of components of dietary foods such as tea, coffee, wine, oils, and honey and the role and mechanism of action of these antioxidants in alleviating type 2 diabetes and neurodegenerative disorders. We aim to provide information about possible alternatives to drug treatments used alone or combined to reduce drug intake and encourage the consumption of natural ingredients at doses adequate to promote health and combat pathologies while reducing unwanted risks and side effects.

Quercetin improves pancreatic cancer chemo-sensitivity by regulating oxidative-inflammatory networks

Chemotherapy is the main method for controlling pancreatic cancer metastasis but the prevalent chemotherapy resistance limits its utilization. The response of oxidation and inflammation often promotes pancreatic cancer progression and chemo-resistance. It is critical to explore the potential natural products with few side effects to control inflammatory responses and understand the related mechanisms. Quercetin is a flavonoid widely found in numerous vegetables, fruits, and foods and is thought to have antioxidant and anti-inflammatory properties, which may be associated with improvement of chemotherapy sensitivity during pancreatic cancer treatment. Quercetin may sensitize pancreatic cancer cells to the chemotherapeutic agents, including bromodomain and extraterminal domain inhibitors (BETI), daunorubicin, gemcitabine, sulforaphane, doxorubicin, and tumor necrosis factor-related signaling apoptosis-inducing ligand (TRAIL). Meanwhile, during the chemo-resistance therapy, many signaling molecules are involved with toll-like receptor 4 (TLR4)-mediated oxidative and inflammatory pathway. The effects of quercetin on other oxidative and inflammatory pathways were also explored. Quercetin may exert antitumor activity during the prevention of pancreatic cancer progression by regulating oxidative and inflammatory networks, which can promote immune escape of cancer cells by inducing immunosuppressive cytokines. Studying these patterns will help us to better understand the functional role of quercetin in the improvement of pancreatic cancer chemo-sensitivity. PRACTICAL APPLICATIONS: Chemotherapy is the major way for treating pancreatic cancer metastasis but the prevalent chemotherapy resistance caused by oxidative and inflammatory responses limits its utilization. It is necessary to explore the potential natural products with few side effects to prevent the oxidative and inflammatory responses. Quercetin is a flavonoid widely found in numerous vegetables, fruits, and foods and is thought to have antioxidant and anti-inflammatory properties, which may be associated with improvement of chemotherapy sensitivity of pancreatic cancer treatment by sensitizing pancreatic cancer cells to various chemotherapeutic agents via the regulation of oxidative and inflammatory networks. Studying these patterns will help us to better understand the functional role of quercetin in the improvement of pancreatic cancer chemo-sensitivity.

An Overview of Herbal-Based Antidiabetic Drug Delivery Systems: Focus on Lipid- and Inorganic-Based Nanoformulations

Diabetes is a metabolic pathology with chronic high blood glucose levels that occurs when the pancreas does not produce enough insulin or the body does not properly use the insulin it produces. Diabetes management is a puzzle and focuses on a healthy lifestyle, physical exercise, and medication. Thus far, the condition remains incurable; management just helps to control it. Its medical treatment is expensive and is to be followed for the long term, which is why people, especially from low-income countries, resort to herbal medicines. However, many active compounds isolated from plants (phytocompounds) are poorly bioavailable due to their low solubility, low permeability, or rapid elimination. To overcome these impediments and to alleviate the cost burden on disadvantaged populations, plant nanomedicines are being studied. Nanoparticulate formulations containing antidiabetic plant extracts or phytocompounds have shown promising results. We herein aimed to provide an overview of the use of lipid- and inorganic-based nanoparticulate delivery systems with plant extracts or phytocompounds for the treatment of diabetes while highlighting their advantages and limitations for clinical application. The findings from the reviewed works showed that these nanoparticulate formulations resulted in high antidiabetic activity at low doses compared to the corresponding plant extracts or phytocompounds alone. Moreover, it was shown that nanoparticulate systems address the poor bioavailability of herbal medicines, but the lack of enough preclinical and clinical pharmacokinetic and/or pharmacodynamic trials still delays their use in diabetic patients.

Carob Extract Supplementation Together with Caloric Restriction and Aerobic Training Accelerates the Recovery of Cardiometabolic Health in Mice with Metabolic Syndrome

Carob, the fruit of Ceratonia siliqua L. exerts antidiabetic, anti-inflammatory, and antioxidant effects and could be a useful strategy for the treatment and/or prevention of metabolic syndrome (MetS). The aim of this study was to analyze whether supplementation with a carob fruit extract (CSAT+®), alone or in combination with aerobic training, accelerates the recovery of cardiometabolic health in mice with MetS subjected to a caloric restriction. For this purpose, mice were fed with a high fat (58% kcal from fat)/high sugar diet for 23 weeks to induce MetS. During the next two weeks, mice with MetS were switched to a diet with a lower caloric content (25% kcal from fat) supplemented or not with CSAT+® (4.8%) and/or subjected to aerobic training. Both caloric reduction and aerobic training improved the lipid profile and attenuated MetS-induced insulin resistance measured as HOMA-IR. However, only supplementation with CSAT+® enhanced body weight loss, increased the circulating levels of adiponectin, and lowered the plasma levels of IL-6. Moreover, CSAT+® supplementation was the only effective strategy to reduce the weight of epidydimal adipose tissue and to improve insulin sensitivity in the liver and in skeletal muscle. Although all interventions improved endothelial function in aorta segments, only supplementation with CSAT+® reduced obesity-induced hypertension, prevented endothelial dysfunction in mesenteric arteries, and decreased the vascular response of aorta segments to the vasoconstrictor AngII. The beneficial cardiometabolic effects of CSAT+® supplementation, alone or in combination with aerobic training, were associated with decreased mRNA levels of pro-inflammatory markers such as MCP-1, TNFα, IL-1β, and IL-6 and with increased gene expression of antioxidant enzymes, such as GSR, GPX-3, and SOD-1 in the liver, gastrocnemius, retroperitoneal adipose tissue, and aorta. In conclusion, supplementation with CSAT+®, alone or in combination with aerobic training, to mice with MetS subjected to caloric restriction for two weeks enhances body weight loss, improves the lipid profile and insulin sensitivity, and exerts antihypertensive effects through its anti-inflammatory and antioxidant properties.

Potential Pharmaceutical Applications of Quercetin in Cardiovascular Diseases

Quercetin, as a member of flavonoids, has emerged as a potential therapeutic agent in cardiovascular diseases (CVDs) in recent decades. In this comprehensive literature review, our goal was a critical appraisal of the pathophysiological mechanisms of quercetin in relation to the classical cardiovascular risk factors (e.g., hyperlipidemia), atherosclerosis, etc. We also assessed experimental and clinical data about its potential application in CVDs. Experimental studies including both in vitro methods and in vivo animal models mainly outline the following effects of quercetin: (1) antihypertensive, (2) hypolipidemic, (3) hypoglycemic, (4) anti-atherosclerotic, and (5) cardioprotective (suppressed cardiotoxicity). From the clinical point of view, there are human studies and meta-analyses implicating its beneficial effects on glycemic and lipid parameters. In contrast, other human studies failed to demonstrate consistent favorable effects of quercetin on other cardiometabolic risk factors such as MS, obesity, and hypertension, underlying the need for further investigation. Analyzing the reason of this inconsistency, we identified significant drawbacks in the clinical trials’ design, while the absence of pharmacokinetic/pharmacodynamic tests prior to the studies attenuated the power of clinical results. Therefore, additional well-designed preclinical and clinical studies are required to examine the therapeutic mechanisms and clinical efficacy of quercetin in CVDs.

Quercetin: A Molecule of Great Biochemical and Clinical Value and Its Beneficial Effect on Diabetes and Cancer

Quercetin belongs to the broader category of polyphenols. It is found, in particular, among the flavonols, and along with kaempferol, myricetin and isorhamnetin, it is recognized as a foreign substance after ingestion in contrast to vitamins. Quercetin occurs mainly linked to sugars with the most common compounds being quercetin-3-O-glucoside or as an aglycone, especially in the plant population. The aim of this review is to present a recent bibliography on the mechanisms of quercetin absorption and metabolism, bioavailability, and antioxidant and the clinical effects in diabetes and cancer. The literature reports a positive effect of quercetin on oxidative stress, cancer, and the regulation of blood sugar levels. Moreover, research-administered drug dosages of up to 2000 mg per day showed mild to no symptoms of overdose. It should be noted that quercetin is no longer considered a carcinogenic substance. The daily intake of quercetin in the diet ranges 10 mg-500 mg, depending on the type of products consumed. This review highlights that quercetin is a valuable dietary antioxidant, although a specific daily recommended intake for this substance has not yet been determined and further studies are required to decide a beneficial concentration threshold.

Should We 'Eat a Rainbow'? An Umbrella Review of the Health Effects of Colorful Bioactive Pigments in Fruits and Vegetables

Health promotion campaigns have advocated for individuals to 'eat a rainbow' of fruits and vegetables (FV). However, the literature has only focused on individual color pigments or individual health outcomes. This umbrella review synthesized the evidence on the health effects of a variety of color-associated bioactive pigments found in FV (carotenoids, flavonoids, betalains and chlorophylls), compared to placebo or low intakes. A systematic search of PubMed, EMBASE, CINAHL and CENTRAL was conducted on 20 October 2021, without date limits. Meta-analyzed outcomes were evaluated for certainty via the GRADE system. Risk of bias was assessed using the Centre for Evidence-Based Medicine critical appraisal tools. A total of 86 studies were included, 449 meta-analyzed health outcomes, and data from over 37 million participants were identified. A total of 42% of health outcomes were improved by color-associated pigments (91% GRADE rating very low to low). Unique health effects were identified: n = 6 red, n = 10 orange, n = 3 yellow, n = 6 pale yellow, n = 3 white, n = 8 purple/blue and n = 1 green. Health outcomes associated with multiple color pigments were body weight, lipid profile, inflammation, cardiovascular disease, mortality, type 2 diabetes and cancer. Findings show that color-associated FV variety may confer additional benefits to population health beyond total FV intake.

The Impact of Flavonols on Cardiovascular Risk

Cardiovascular disease (CVD) is the leading cause of deaths globally. The main target for prevention of cardiovascular (CV) risk are lifestyle changes, including particular dietary recommendations, involving high intake of fruits and vegetables. Flavonols are a subgroup of flavonoids—compounds present in fruits, vegetables, and tea—known for their antioxidative properties. There are many findings about the beneficial impact of flavonols on general CV risk and its factors, but mainly from in vitro and animal model studies. This paper summarizes data from human studies about flavonols’ impact on general CV risk and its factors. A high dietary intake of flavonols could decrease CVD mortality directly or through impact on selected CV factors; however, available data are inconsistent. Nonetheless, specific groups of patients (smoking men, hypertensive and diabetic patients) can potentially benefit from selected dietary modifications or flavonols (quercetin) supplementation. Future investigations about kaempferol and myricetin are needed.

Quercetin: an effective polyphenol in alleviating diabetes and diabetic complications

Various studies, especially in recent years, have shown that quercetin has beneficial therapeutic effects in various human diseases, including diabetes. Quercetin has significant anti-diabetic effects and may be helpful in lowering blood sugar and increasing insulin sensitivity. Quercetin appears to affect many factors and signaling pathways involved in insulin resistance and the pathogenesis of type 2 of diabetes. TNFα, NFKB, AMPK, AKT, and NRF2 are among the factors that are affected by quercetin. In addition, quercetin can be effective in preventing and ameliorating the diabetic complications, including diabetic nephropathy, cardiovascular complications, neuropathy, delayed wound healing, and retinopathy, and affects the key mechanisms involved in the pathogenesis of these complications. These positive effects of quercetin may be related to its anti-inflammatory and anti-oxidant properties. In this article, after a brief review of the pathogenesis of insulin resistance and type 2 diabetes, we will review the latest findings on the anti-diabetic effects of quercetin with a molecular perspective. Then we will review the effects of quercetin on the key mechanisms of pathogenesis of diabetes complications including nephropathy, cardiovascular complications, neuropathy, delayed wound healing, and retinopathy. Finally, clinical trials investigating the effect of quercetin on diabetes and diabetes complications will be reviewed.

Antidiabetic Phytochemicals From Medicinal Plants: Prospective Candidates for New Drug Discovery and Development

Diabetes, a chronic physiological dysfunction affecting people of different age groups and severely impairs the harmony of peoples' normal life worldwide. Despite the availability of insulin preparations and several synthetic oral antidiabetic drugs, there is a crucial need for the discovery and development of novel antidiabetic drugs because of the development of resistance and side effects of those drugs in long-term use. On the contrary, plants or herbal sources are getting popular day by day to the scientists, researchers, and pharmaceutical companies all over the world to search for potential bioactive compound(s) for the discovery and development of targeted novel antidiabetic drugs that may control diabetes with the least unwanted effects of conventional antidiabetic drugs. In this review, we have presented the prospective candidates comprised of either isolated phytochemical(s) and/or extract(s) containing bioactive phytoconstituents which have been reported in several in vitro, in vivo, and clinical studies possessing noteworthy antidiabetic potential. The mode of actions, attributed to antidiabetic activities of the reported phytochemicals and/or plant extracts have also been described to focus on the prospective phytochemicals and phytosources for further studies in the discovery and development of novel antidiabetic therapeutics.

Quercetin for managing type 2 diabetes and its complications, an insight into multitarget therapy

BACKGROUND

Quercetin, a bioflavonoid abundant in grapefruit, onion, berries, etc., has vast therapeutic potential, especially against Type 2 diabetes and its complications. Quercetin showed similar effects as that of metformin, (widely prescribed antidiabetic drug) in cell lines models (Sajan et al., 2010; Dhanya et al., 2017). In vivo findings also showcase it as a promising agent against diabetes and its pathophysiological complications.

SCOPE AND APPROACH

Quercetin can be produced on a large scale through a novel fermentation-based glycosylation strategy from cheap substrates and can be utilized as a dietary supplement. The review focuses on the mounting evidence pointing to Quercetin as a promising candidate for managing type 2 diabetes and its oxidative stress mediated pathophysiological complications.

CONCLUSION

Quercetin acts on multiple targets of diabetes and regulates key signalling pathways which improve the symptoms as well as the complications of Type 2 diabetes. However further studies are needed to improve the bioavailability and to establish a dosing regimen for Quercetin.

Mechanisms Underlying the Antidiabetic Activities of Polyphenolic Compounds: A Review

Polyphenolic compounds are thought to show considerable promise for the treatment of various metabolic disorders, including type 2 diabetes mellitus (T2DM). This review addresses evidence from in vitro, in vivo, and clinical studies for the antidiabetic effects of certain polyphenolic compounds. We focus on the role of cytotoxic human amylin (hA) aggregates in the pathogenesis of T2DM, and how polyphenols can ameliorate this process by suppressing or modifying their formation. Small, soluble amylin oligomers elicit cytotoxicity in pancreatic islet β-cells and may thus cause β-cell disruption in T2DM. Amylin oligomers may also contribute to oxidative stress and inflammation that lead to the triggering of β-cell apoptosis. Polyphenols may exert antidiabetic effects via their ability to inhibit hA aggregation, and to modulate oxidative stress, inflammation, and other pathways that are β-cell-protective or insulin-sensitizing. There is evidence that their ability to inhibit and destabilize self-assembly by hA requires aromatic molecular structures that bind to misfolding monomers or oligomers, coupled with adjacent hydroxyl groups present on single phenyl rings. Thus, these multifunctional compounds have the potential to be effective against the pleiotropic mechanisms of T2DM. However, substantial further research will be required before it can be determined whether a polyphenol-based molecular entity can be used as a therapeutic for type 2 diabetes.

The roles of quercetin in diabetes mellitus and related metabolic disorders; special focus on the modulation of gut microbiota: A comprehensive review

Quercetin is a dietary flavonoid that can affect the balance between anti-oxidant defense system and oxidative stress. A number of studies showed the positive effects of quercetin on diabetes mellitus and related metabolic disorders through different pathways such as gut flora. However, findings are conflicting. In addition, it seems no studies have summarized all potential mechanisms of quercetin in diabetes mellitus, so far. Therefore, the aims of the present comprehensive review were to provide an overview on biological and biochemical characteristics of quercetin and investigate the effect of quercetin on diabetes mellitus and related metabolic disorders by focusing on its effects on the modulation of gut microbiota. For this purpose, findings of In vitro, animal studies, clinical trials, and review studies with the English language published until January 2021 were summarized. They were identified through electronic databases (PubMed, Scopus, and Cochrane Library) and Google Scholar. Findings showed that quercetin can be an effective component for improving glycemic status and other metabolic disorders related to diabetes mellitus based on In vitro and animal studies. However, environmental factors, food processing and using nanoformulations can affect its efficacy in human studies. Several potential mechanisms, including the modulation of gut flora are proposed for its actions. However, due to limited clinical trials and contradictory findings, more high-quality clinical trials are needed to make a decision on the efficacy of supplementation with quercetin as a complementary therapy for the management of diabetes mellitus, metabolic disorders, and modulating gut flora.

Natural Polyphenols as Immunomodulators to Rescue Immune Response Homeostasis: Quercetin as a Research Model against Severe COVID-19

The COVID-19 pandemic is caused by SARS-CoV-2 and is leading to the worst health crisis of this century. It emerged in China during late 2019 and rapidly spread all over the world, producing a broad spectrum of clinical disease severity, ranging from asymptomatic infection to death (4.3 million victims so far). Consequently, the scientific research is devoted to investigating the mechanisms of COVID-19 pathogenesis to both identify specific therapeutic drugs and develop vaccines. Although immunological mechanisms driving COVID-19 pathogenesis are still largely unknown, new understanding has emerged about the innate and adaptive immune responses elicited in SARS-CoV-2 infection, which are mainly focused on the dysregulated inflammatory response in severe COVID-19. Polyphenols are naturally occurring products with immunomodulatory activity, playing a relevant role in reducing inflammation and preventing the onset of serious chronic diseases. Mainly based on data collected before the appearance of SARS-CoV-2, polyphenols have been recently suggested as promising agents to fight COVID-19, and some clinical trials have already been approved with polyphenols to treat COVID-19. The aim of this review is to analyze and discuss the in vitro and in vivo research on the immunomodulatory activity of quercetin as a research model of polyphenols, focusing on research that addresses issues related to the dysregulated immune response in severe COVID-19. From this analysis, it emerges that although encouraging data are present, they are still insufficient to recommend polyphenols as potential immunomodulatory agents against COVID-19.

Caloric Restriction Mimetics in Nutrition and Clinical Trials

The human diet and dietary patterns are closely linked to the health status. High-calorie Western-style diets have increasingly come under scrutiny as their caloric load and composition contribute to the development of non-communicable diseases, such as diabetes, cancer, obesity, and cardiovascular disorders. On the other hand, calorie-reduced and health-promoting diets have shown promising results in maintaining health and reducing disease burden throughout aging. More recently, pharmacological Caloric Restriction Mimetics (CRMs) have gained interest of the public and scientific community as promising candidates that mimic some of the myriad of effects induced by caloric restriction. Importantly, many of the CRM candidates activate autophagy, prolong life- and healthspan in model organisms and ameliorate diverse disease symptoms without the need to cut calories. Among others, glycolytic inhibitors (e.g., D-allulose, D-glucosamine), hydroxycitric acid, NAD+ precursors, polyamines (e.g., spermidine), polyphenols (e.g., resveratrol, dimethoxychalcones, curcumin, EGCG, quercetin) and salicylic acid qualify as CRM candidates, which are naturally available via foods and beverages. However, it is yet unclear how these bioactive substances contribute to the benefits of healthy diets. In this review, we thus discuss dietary sources, availability and intake levels of dietary CRMs. Finally, since translational research on CRMs has entered the clinical stage, we provide a summary of their effects in clinical trials.

Phytonutrient supplements and metabolic biomarkers of cardiovascular disease: An umbrella review of meta-analyses of clinical trials

Phytonutrients exert several pharmacological effects on humans. In this study, we performed an umbrella review of the association of phytonutrient supplements (PNSs) with biomarkers of cardiovascular disease. Relevant published systematic reviews and meta-analyses of clinical trials were identified by searching PubMed, Embase, and Cochrane Library until July 4, 2020. Weighted mean differences (WMDs) and 95% confidence intervals (CIs) for summarized effects and I2 statistics of heterogeneity were extracted from individual studies or reanalyzed using a random-effects model. Of the 50 included studies, pooled effects of PNSs on blood pressure, lipid profiles, and glycemic control were reported in 16, 25, and 14 articles, respectively. The findings appeared to be highly heterogeneous among individual trials of included systematic reviews and meta-analyses. Ginger (WMD = -6.36 mmHg, 95% CI = -11.27, -1.46) and Hibiscus sabdariffa (WMD = -7.58 mmHg, 95% CI = -9.69, -5.46) were associated with lowered systolic blood pressure, whereas Aloe vera, Nigella sativa, and spirulina were associated with beneficial effects on both lipid profiles and glycemic control. In summary, this umbrella review has provided up-to-date evidence for the effect of PNSs on biomarkers related to hypertension, dyslipidemia, and diabetes. The results must be interpreted with caution due to potential heterogeneity.

The Therapeutic Effects and Mechanisms of Quercetin on Metabolic Diseases: Pharmacological Data and Clinical Evidence

Metabolic diseases have become major public health issues worldwide. Searching for effective drugs for treating metabolic diseases from natural compounds has attracted increasing attention. Quercetin, an important natural flavonoid, is extensively present in fruits, vegetables, and medicinal plants. Due to its potentially beneficial effects on human health, quercetin has become the focus of medicinal attention. In this review, we provide a timely and comprehensive summary of the pharmacological advances and clinical data of quercetin in the treatment of three metabolic diseases, including diabetes, hyperlipidemia, and nonalcoholic fatty liver disease (NAFLD). Accumulating evidences obtained from animal experiments prove that quercetin has beneficial effects on these three diseases. It can promote insulin secretion, improve insulin resistance, lower blood lipid levels, inhibit inflammation and oxidative stress, alleviate hepatic lipid accumulation, and regulate gut microbiota disorders in animal models. However, human clinical studies on the effects of quercetin in diabetes, hyperlipidemia, and NAFLD remain scarce. More clinical trials with larger sample sizes and longer trial durations are needed to verify its true effectiveness in human subjects. Moreover, another important issue that needs to be resolved in future research is to improve the bioavailability of quercetin. This review may provide valuable information for the basic research, drug development, and clinical application of quercetin in the treatment of metabolic diseases.

Natural products and analogs as preventive agents for metabolic syndrome via peroxisome proliferator-activated receptors: An overview

Natural products and synthetic analogs have drawn much attention as potential therapeutical drugs to treat metabolic syndrome. We reviewed the underlying mechanisms of 32 natural products and analogs with potential pharmacological effects in vitro, and especially in rodent models and/or patients, that usually act on the PPAR pathway, along with other molecular targets. Recent outstanding total syntheses or semisyntheses of these lead compounds are stated. In general, they can activate the transcriptional activity of PPARα, PPARγ, PPARα/γ, PPARβ/δ, PPARα/δ, PPARγ/δ and panPPAR as weak, partial agonists or selective PPARγ modulators (SPPARγM), which may be useful for managing obesity, type 2 diabetes (T2D), dyslipidemia and non-fatty liver disease (NAFLD). Terpenoids is the largest group of compounds that act as potential modulators on PPARs and are comprised from small lipophilic cannabinoids to lipophilic pentacyclic triterpenes and polar saponins. Shikimates-phenylpropanoids include polar heterocyclic flavonoids and phenolic compounds containing at least one C3-C6 unit and usually a double bond on the propyl chain. Quercetin (19), resveratrol (24) and curcumin (27), stand out from this group for exhibiting beneficial effects on patients. Alkaloids, the minor group of potential modulators on PPARs, include berberine (30), which has been widely explored in preclinical and clinical studies for its potential beneficial effects on T2D and dyslipidemia. However, large-scale clinical trials may be warranted for the promising compounds.

New insight into the role of isorhamnetin as a regulator of insulin signaling pathway in type 2 diabetes mellitus rat model: Molecular and computational approach

We intended to examine the molecular mechanism of action of isorhamnetin (IHN) to regulate the pathway of insulin signaling. Molecular analysis, immunofluorescence, and histopathological examination were used to assess the anti-hyperglycemic and insulin resistance lowering effects of IHN in streptozotocin /high fat diet-induced type 2 diabetes using Wistar rats. At the microscopic level, treatment with IHN resulted in the restoration of myofibrils uniform arrangement and adipose tissue normal architecture. At the molecular level, treatment with IHN at three different doses showed a significant decrease in m-TOR, IGF1-R & LncRNA-RP11-773H22.4. expression and it up-regulated the expression of AKT2 mRNA, miR-1, and miR-3163 in both skeletal muscle and adipose tissue. At the protein level, IHN treated group showed a discrete spread with a moderate faint expression of m-TOR in skeletal muscles as well as adipose tissues. We concluded that IHN could be used in the in ameliorating insulin resistance associated with type 2 diabetes mellitus.

Effect of quercetin supplementation on plasma lipid profiles, blood pressure, and glucose levels: a systematic review and meta-analysis

CONTEXT

Clinical trials examining the cardiovascular protective effects of quercetin in humans have reported conflicting results.

OBJECTIVE

The aim of this systematic review was to summarize evidence of the effects of quercetin supplementation on plasma lipid profiles, blood pressure (BP), and glucose levels in humans by performing a meta-analysis of randomized controlled trials.

DATA SOURCES

MEDLINE, Embase, and Scopus databases were searched electronically from their inception to July 2018 to identify randomized controlled trials that assessed the impact of quercetin on lipid profiles, BP, and glucose levels.

STUDY SELECTION

Randomized controlled trials assessing the effects of quercetin or a standardized quercetin-enriched extract on plasma lipid profiles, BP, and glucose levels in humans were eligible for inclusion.

DATA EXTRACTION

A random-effects model was used for data analysis. Continuous variables were expressed as weighted mean differences (WMDs) and 95%CIs. Subgroup analyses were conducted to explore possible influences of study characteristics. Sensitivity analyses were also performed, as were analyses of publication bias.

RESULTS

Seventeen trials (n = 896 participants total) were included in the overall analysis. Pooled results showed that quercetin significantly lowered both systolic BP (WMD, -3.09 mmHg; 95%CI, -4.59 to -1.59; P = 0.0001) and diastolic BP (WMD, -2.86 mmHg; 95%CI, -5.09 to -0.63; P = 0.01). Neither lipid profiles nor glucose concentrations changed significantly. In subgroup analyses, significant changes in high-density lipoprotein cholesterol and triglycerides were observed in trials with a parallel design and in which participants consumed quercetin for 8 weeks or more.

CONCLUSION

Quercetin intake resulted in significantly decreased BP in humans. Moreover, participants who consumed quercetin for 8 weeks or more showed significantly changed levels of high-density lipoprotein cholesterol and triglycerides in trials with a parallel design.

Effects of Polyphenols on Insulin Resistance

Insulin resistance (IR) is apparent when tissues responsible for clearing glucose from the blood, such as adipose and muscle, do not respond properly to appropriate signals. IR is estimated based on fasting blood glucose and insulin, but some measures also incorporate an oral glucose challenge. Certain (poly)phenols, as supplements or in foods, can improve insulin resistance by several mechanisms including lowering postprandial glucose, modulating glucose transport, affecting insulin signalling pathways, and by protecting against damage to insulin-secreting pancreatic β-cells. As shown by intervention studies on volunteers, the most promising candidates for improving insulin resistance are (-)-epicatechin, (-)-epicatechin-containing foods and anthocyanins. It is possible that quercetin and phenolic acids may also be active, but data from intervention studies are mixed. Longer term and especially dose-response studies on mildly insulin resistant participants are required to establish the extent to which (poly)phenols and (poly)phenol-rich foods may improve insulin resistance in compromised groups.

Study on the Mechanisms of Banxia Xiexin Decoction in Treating Diabetic Gastroparesis Based on Network Pharmacology

In China, Banxia Xiexin decoction (BXD) is applied to treat diabetic gastroparesis (DGP), but its key active ingredients and mechanisms against DGP are unclear. This study is designated to reveal the molecular mechanisms of BXD in treating DGP by adopting a creative approach known as network pharmacology to explore the active ingredients and therapeutic targets of BXD. In our study, 730 differentially expressed genes of DGP were obtained, and 30 potential targets of BXD against DGP were screened out (including ADRB2, DRD1, FOS, MMP9, FOSL1, FOSL2, JUN, MAP2, DRD2, MYC, F3, CDKN1A, IL6, NFKBIA, ICAM1, CCL2, SELE, DUOX2, MGAM, THBD, SERPINE1, ALOX5, CXCL11, CXCL2, CXCL10, RUNX2, CD40LG, C1QB, MCL1, and ADCYAP1). Based on the findings, BXD contains 60 compounds with therapeutic effect on DGP, including the key active ingredients such as quercetin, wogonin, baicalein, beta-sitosterol, and kaempferol. Sixty-eight pathways including TNF signaling pathway, IL-17 signaling pathway, and AGE-RAGE signaling pathway were significantly enriched. In this study, the mechanisms of BXD in treating DGP are affirmed to be a complex network with multi-target and multi-pathway, which provides a reference for future experimental studies.

Therapeutic Potential of Quercetin: New Insights and Perspectives for Human Health

Quercetin (Que) and its derivatives are naturally occurring phytochemicals with promising bioactive effects. The antidiabetic, anti-inflammatory, antioxidant, antimicrobial, anti-Alzheimer's, antiarthritic, cardiovascular, and wound-healing effects of Que have been extensively investigated, as well as its anticancer activity against different cancer cell lines has been recently reported. Que and its derivatives are found predominantly in the Western diet, and people might benefit from their protective effect just by taking them via diets or as a food supplement. Bioavailability-related drug-delivery systems of Que have also been markedly exploited, and Que nanoparticles appear as a promising platform to enhance their bioavailability. The present review aims to provide a brief overview of the therapeutic effects, new insights, and upcoming perspectives of Que.

Targeting Casein kinase 2 with quercetin or enzymatically modified isoquercitrin as a strategy for boosting the type 1 interferon response to viruses and promoting cardiovascular health

The serine/threonine kinase CK2 has been shown to down-regulate the production of type 1 interferons in response to viral infections by conferring an inhibitory phosphorylation on RIG-I, which functions to detect double-stranded RNA generated during replication of RNA viruses. Quercetin and certain other planar flavones/flavonols can inhibit CK2 in high nanomolar concentrations; this may explain quercetin's ability to slow the proliferation of RNA viruses in cell cultures and in mice. Limited clinical evidence suggests that supplemental quercetin may decrease risk for upper respiratory infections in humans. Quercetin and enzymatically-modified isoquercitrin (EMIQ - a food additive/nutraceutical that upon oral administration achieves far higher plasma concentrations of quercetin than quercetin per se) also have exerted a range of vascular-protective effects clinically and in rodents - improving endothelial function, warding off atherosclerosis, lowering blood pressure, decreasing C-reactive protein, aiding glycemic control, stabilizing platelets - that might also, at least in part, reflect CK2 inhibition. The utility of quercetin, EMIQ, and other clinically feasible CK2 inhibitors for aiding control of viral infections and promoting vascular and metabolic health merits further evaluation.

Relation of Fruits and Vegetables with Major Cardiometabolic Risk Factors, Markers of Oxidation, and Inflammation

Noncommunicable diseases (NCDs) are considered to be the leading cause of death worldwide. Inadequate fruit and vegetable intake have been recognized as a risk factor for almost all NCDs (type 2 diabetes mellitus, cancer, and cardiovascular and neurodegenerative diseases). The main aim of this review is to examine the possible protective effect that fruit and vegetable consumption or their bioactive compounds may have on the development of NCDs such as atherosclerosis. The accumulated evidence on the protective effects of adequate consumption of fruits and vegetables in some cases, or the lack of evidence in others, are summarized in the present review. The main conclusion of this review is that well-designed, large-scale, long-term studies are needed to truly understand the role fruit and vegetable consumption or their bioactive compounds have in atherosclerosis.